Sharpe ratio and information ratio

[andrewphillipsn]

Describe the problem.
Provide an implementation for sharpe ratio and information ratio calculations in gs_quant.

Describe the solution you'd like
Information ratio should calculate the rolling return per unit volatility of a series versus a benchmark series. Sharpe ratio calculation should compute rolling return per unit volatility of a series versus risk free rate for currency of the target series (i.e excess return). Both of these measures should calculate excess return daily with correct holiday / interpolation handling

Are you willing to contribute
Yes

Additional context
Needs full regtesting. Identify correct data sources for risk free rates

[stephen-183]

Proposed signatures
sharpe_ratio(prices: Series, rate: Union[Asset, Number], *, day_count_convention) -> Series
information_ratio(prices: Series, benchmark[Index], *, day_count_convention) -> Series
excess_return(prices: Series, benchmark_or_rate: Union[Asset, Number], *, day_count_convention) -> Series

[andrewphillipsn]

@stephen-183 benchmark can be non-index, so I would use Asset

[andrewphillipsn]

@stephen-183 or a list of valid types (e.g. Index, Stock, etc)

[stephen-183]

Makes sense; I'll use Asset to be concise.
information_ratio(prices: Series, benchmark[Asset], *, day_count_convention) -> Series